I favor approaches to morality that make reference to human nature like natural law theory (for an overview natural law theory in relation to social justice go here) and natural virtue ethics (for some virtue ethics insights in relation to Plato go here). There are plenty of questions or objections that can be raised here: do we even have a nature? If so, what is it? Even if we have one, can we really know it? Don’t all the diversity, disagreement, and situational differences we encounter suggest we can’t find some universal, objective, and intelligible shared traits? What about the darker aspects of human nature? How would they fit into our moral theory grounded in human nature? And can we really identify goodness with any natural property whether pleasure, reason, social capacity, love, or whatever?
These are all important objections. But perhaps the most famous objection to such human nature-based approaches was raised by the Scottish philosopher David Hume (1711-76). Hume observed that there are three ways something can be considered natural: (1) opposed to supernatural or miraculous; (2) normal as opposed to unusual or rare; and (3) not artificial or made by humans. He argued that, regardless of the sense of natural we employ, we cannot immediately derive anything about value from a fact; we “cannot derive an ought from an is”. This means we cannot logically deduce anything about what we ought to do just from the discovery that we in fact do it. Here is an example of a prescriptive conclusion inferred from a descriptive premise:
Example: Doing excessive drugs can prevent proper mental functioning. Therefore it is wrong to do excessive amounts of drugs.
Hume would claim this inference is fallacious, that is, not logical. Now it is certainly true that a prescriptive conclusion cannot be logically deduced from a premise that is only descriptive. That is, if we are using a form of argumentation called deduction—a form of argument that states if the premises are true then the conclusion is guaranteed to be true as well—we have an invalid inference. After all, we can clearly see that there is a gap between, say, the fact of human aggression being natural and any prescription of aggression as moral or immoral. The conclusion is not guaranteed as true even if the premise is true.
However, a natural law theorist doesn’t need to provide fallacious arguments that only have a factual description(s) as a premise. One can add, along with a descriptive premise, one or more prescriptive premises. For example, we could construct this valid argument by adding a natural law premise to the example above:
Premise 1: Doing excessive drugs can prevent proper mental functioning.
Premise 2: Improper mental functioning is bad since it thwarts the actualization of our natural rational potential.
Therefore it is wrong to do excessive amounts of drugs.
So we don’t need to immediately infer an ought from an is, or a moral prescription from a factual description; rather, we can add a prescriptive premise to the argument to draw a valid prescriptive conclusion.
We should also note that we can infer a prescription from a descriptive premise alone if we are using an inductive argument rather than a deductive argument. An inductive argument, unlike a deductive one, gives some evidence for a more or less probable conclusion—it doesn’t promise a guaranteed conclusion. So if we are only seeking a highly probable conclusion, which for some is fine when it comes to the subject matter of ethics, we may proceed and infer a prescription from a description after all.
Moreover, many natural law theorists and natural virtue ethicists can point out that our understanding of what is good is not something we infer logically or illogically from a fact or set of facts. Rather, we analyze human nature and then come to immediately see the good in a manner that is self-evident once all the relevant factors are understood (for example, we see that reason or our capacity to enter into meaningful social relationships is self-evidently good). Thus the value judgment in premise two of the above argument—improper mental functioning is bad since it thwarts the actualization of our natural rational potential—would ultimately be justified with an appeal to self-evidence. This strategy of focusing on the immediate self-evidence of natural goods, since it avoids inference, might make Hume’s objection – that prescriptions which flow from descriptions of human nature are grounded in fallacious inferences – irrelevant.
Alternatively, a natural law theorist could try and undermine the very distinction on which the naturalistic fallacy rests. Perhaps facts cannot be separated from values in the first place; perhaps facts, such as how the body or mind works, are the effects of God’s design—a design that is itself a function of various evaluations God made. If one takes this theistic approach to natural law, then one can argue that we don’t fallaciously derive an ought from an is; rather, we look at certain natural facts to see how God planned it that way for the good—to see the God-given value in the facts. A similar approach could be taken if one believes in the soul and thinks that the soul is the active form of the body—a form that purposefully guides the development of the physical facts. And perhaps a naturalistic account of natural teleology could, against the currently prevailing tendencies, be given that would undermine the fact/value distinction without theism and dualism. Indeed, some American pragmatists, such as John Dewey, attempted to do just this.
In any case, these are some ways to respond to Hume’s challenge to moral theories that start with a description of human nature and move to prescriptions, whether law-like (as in the case of natural law theory) or in the form of flexible guides (as in virtue ethics). Are any of these successful? If not, why? Are there other strategies that can be employed to face the challenge?